more context please Niels...
so, usually you add a style file to the <head> section of a page. This is done for you by NetTalk using one of the template settings in web server (the list of style files.) Now that list can contain variables, but those variables need to be loaded before it's used.
This will add that style to the whole site (presumably for all users.)
Now if you want to add the style for just a specific page, or control, or user or whatever then I need to know more to give you a specific answer.
cheers
Bruce